When a picture is taken on the basis of a value measured by an incident light exposure meter or flash meter, the light is measured in the vicinity of an object or person to be photographed and the measuring place is distant from the picture taking or camera place. Accordingly, the photographer must move between the two places, to measure the light at the measuring position and to set exposure conditions and release the camera shutter at the camera position. Thus, such picture taking requires complex operation. To cope with such a trouble, a camera data transmission system has been proposed in a Japanese laid-open patent application with a laid open number 52-58529. In the system, an external exposure meter can be connected through a cable with a camera which is provided with a built-in exposure meter and the camera, when the external exposure meter is connected therewith, controls its exposure in accordance with the light measurement data measured by the external exposure meter at a place distant from the camera and captured by the camera, with the light measurement data from the built-in exposure meter being replaced thereby. However, the prior art system requires a cable for connecting the external exposure meter with the camera and is inconvenient in that the cable sometimes disturbs the measuring operation and that the length of the cable restricts the distance from the camera to a place where the measurement can be made. Additionally, although the light measurement data from the external exposure meter is automatically input to the camera, the setting of an exposure time and a diaphragm aperture value and the shutter release operation must be made manually. Accordingly, when the photographer wishes to take a picture with a desired exposure time or diaphragm aperture for his or her desired photographic effect, or when he or she suddenly comes across a change for shutter releasing during the measurement, he or she must return to the camera position to manually set the exposure condition and/or depress the shutter release button. Thus, the system still requires troublesome operation.
Further, the camera of the prior art system is provided with a power switch which is operated independently of the depression of the shutter release button to actuate the camera exposure measuring and calculating circuit, such that the camera can capture the light measurement data from the external meter at any time instead of the data of the built-in exposure meter. The camera is arranged such that it maintains the light measuring operation with the built-in exposure meter while the power switch is closed to effect power supply. In the case when a picture is taken on the basis of the light measurement data fed from the external exposure meter, the built-in exposure meter makes vain measurement and the electric power is wasted from turning-on of the power switch till the light measurement being made by the external exposure meter.
In the prior art system, the external flash meter is not to be connected with the camera. Even if the system is arranged such that flash meter can be connected with the camera with data from daylight photography and flash light photography being selectively input to the camera, following inconvenience is expected. Electronic flash devices are generally constructed to start its light emission, when coupled with cameras, in response to a light emission instruction signal from the camera such as an X contact closure signal produced upon fully opening of the camera shutter. Accordingly, when the combination of the camera and the electronic flash device is desired to be switched from the flash photography condition wherein the flash device is fired upon photography, to the daylight photography wherein a picture is taken without the firing of the flash device, a manual operation for disabling the flash device is required, such as decoupling the flash device from the camera or turning off the switch of the flash device. Manual operation is also required when the combination is switched from the daylight photography to the flash photography mode. Thus, although the system dispenses with the trouble of reading the indication of the exposure meter and manually setting the exposure condition, it still requires a manual operation for the switching of the photography mode, resulting in the remaining of complexity of operation.
Many cameras have been put into practice which have a function of measuring the object brightness passing through the camera objective lens and reflected by the film plane during the film exposure, i.e., during the camera operation, i.e., the function of TTL direct light measuring, and which supplies a flash firing interruption signal to the flash device when the integration of the light measurement reaches a given level. On the other hand, the flash meter is used for measuring the amount of flash light with the flash device being fired independently prior to the camera operation, in order to determine the exposure condition for a particular photographic effect wherein a desired exposure is given with the flash light to a desired portion of the object to be photographed. Hence, the TTL direct light measurement is effected at a different time from the flash light measurement by means of the flash meter. When the amount of flash light is measured with the flash meter, the camera is not in operation, i.e., the camera does not work with no flash light interruption signal being output. At that time, the flash device is fired prior to a camera operation to emit a given amount of flash light and the flash meter calculates, on the basis of the measurement of the given flash light amount, an exposure control data such as a diaphragm aperture value or an exposure time with which a desired exposure is given for a desired portion of an object to be photographed. Thus, a flash photography is made in accordance with predetermined data such as the exposure control data calculated by the flash meter, a desired photography is effected if the flash device emits the same amount of light as that at the time of the measurement and calculation by means of the flash meter. However, it is likely to occur that the flash photography system that controls the flash light amount on the basis of the TTL direct light measurement, will generate a flash light interruption signal at a time when the amount of the emitted flash light reaches a value different from the value of the amount at the time of the prior flash light measurement, since the TTL direct light measuring section of the camera is different from the light receiving portion of the flash meter, in the light acceptance angle and viewing portion in the object to be photographed. Thus, the amount of light emitted upon photography differs from the light amount at the time of measurement by means of the flash meter and the probability of undesired exposure is high.